Ambient light eye illumination for eye-tracking in near-eye display

ABSTRACT

Techniques disclosed herein relate to eye illumination for eye tracking in a near-eye display system. One example of an eye illumination system includes a substrate transparent to visible light and infrared light and configured to be placed in front of an eye of a user, and a shortwave-pass filter on a first surface of the substrate. The shortwave-pass filter includes regions configured to transmit visible light and reflect infrared light in ambient light, and a plurality of windows configured to transmit both visible light and infrared light in the ambient light.

BACKGROUND

An artificial reality system, such as a head-mounted display (HMD) orheads-up display (HUD) system, generally includes a near-eye displaysystem in the form of a headset or a pair of glasses and configured topresent content to a user via an electronic or optic display within, forexample, about 10-20 mm in front of the user's eyes. The near-eyedisplay system may display virtual objects or combine images of realobjects with virtual objects, as in virtual reality (VR), augmentedreality (AR), or mixed reality (MR) applications. For example, in an ARsystem, a user may view both images of virtual objects (e.g.,computer-generated images (CGIs)) and the surrounding environment by,for example, seeing through transparent display glasses or lenses (oftenreferred to as optical see-through) or viewing displayed images of thesurrounding environment captured by a camera (often referred to as videosee-through).

To provide a more immersive artificial reality experience, someartificial reality systems may include an input device for receivinguser inputs, such as hand and/or finger movements. Additionally oralternatively, artificial reality systems can employ eye-trackingsystems that can track the user's eye (e.g., gaze direction). Theartificial reality systems may then employ the gaze directioninformation and/or information gained from the input device to modify orgenerate content based on the direction in which the user is looking,thereby providing a more immersive experience for the user. Eye-trackingsystems can also be used for foveated rendering, foveated compressionand transmission of image data, alertness monitoring, etc.

SUMMARY

This disclosure relates generally to eye tracking in near-eye displaysystems. According to certain embodiments, infrared (IR) spectrum (e.g.,750-2500 nm) of the ambient light can be used to illuminate the user'seyes for eye tracking. In some implementations, a near-eye displaysystem including a shortwave-pass (SWP) filter with a one-dimensional ortwo-dimensional array of windows (or apertures, which can allow the IRlight to pass through) may be placed in front of the user's eye. Assuch, the filter may allow visible light in the ambient light to passthrough any area of the filter and may only allow IR light in theambient light to pass through the array of windows. Therefore, eachwindow (or aperture) may transmit the IR light in the ambient light, andthus may act as a point IR light source. In this way, an array of IRpoint sources may be formed by the array of windows on the SWP filter toilluminate the user's eye. In some implementations, a hot mirror coatingmay be deposited on the surface of or embedded in a transparentsubstrate to perform the SWP filtering function. In some embodiments,the near-display system may include one or more light sources foreye-tracking, where the one or more light sources may be turned on whenthe ambient light is not sufficiently strong for eye illumination andmay be turned off when the ambient light is strong.

According to some embodiments, an eye illumination system for eyetracking in a near-eye display system may include a substratetransparent to visible light and infrared light and configured to beplaced in front of an eye of a user, and a shortwave-pass filter on afirst surface of the substrate. The shortwave-pass filter may includeregions configured to transmit visible light and reflect infrared lightin ambient light, and a plurality of windows configured to transmit bothvisible light and infrared light in the ambient light.

In some embodiments, the shortwave-pass filter may include a pluralityof dielectric layers, a diffractive optical element, or a reflectivematerial layer. In some embodiments, the shortwave-pass filter may beconfigured to reflect ambient light within a wavelength range between750 nm and 2500 nm.

In some embodiments, the plurality of windows may be arranged accordingto a two-dimensional pattern. In some embodiments, the plurality ofwindows may be arranged on circumferences of two or more areas of theshortwave-pass filter. The two or more areas may include an overlappedregion. In some embodiments, each window of the plurality of windows maybe characterized by a diameter equal to or less than 200 μm.

In some embodiments, the eye illumination system may further include anantireflective layer on a second surface of the substrate opposite tothe first surface or on the shortwave-pass filter. In some embodiments,the eye illumination system may also include a second shortwave-passfilter on a second surface of the substrate opposite to the firstsurface, where the second shortwave-pass filter may include regionsconfigured to transmit visible light and reflect infrared light, and mayinclude a set of windows configured to transmit both visible light andinfrared light. In some embodiments, the plurality of windows of theshortwave-pass filter on the first surface of the substrate may bealigned with the set of windows of the second shortwave-pass filter onthe second surface of the substrate. In some embodiments, a total areaof the plurality of windows of the shortwave-pass filter on the firstsurface of the substrate may be greater than a total area of the set ofwindows of the second shortwave-pass filter on the second surface of thesubstrate.

In some embodiments, the substrate may include a curved or a flatsurface. In some embodiments, the substrate may include at least one ofa glass, quartz, plastic, polymer, ceramic, or crystal. In someembodiments, the eye illumination system may also include a light sourceconfigured to illuminate the eye of the user, and a control circuitconfigured to turn off the light source upon determining that a lightintensity of the ambient light is greater than a threshold value.

According to certain embodiments, an eye-tracking system in a displaydevice may include an infrared camera, a substrate transparent tovisible light and infrared light and configured to be placed in front ofan eye of a user of the display device, and a shortwave-pass filter on afirst surface of the substrate. The shortwave-pass filter may includeregions configured to transmit visible light and reflect infrared lightin ambient light, and a plurality of windows configured to transmitinfrared light in the ambient light towards the eye of the user. Theinfrared camera may be configured to capture infrared light reflected bythe eye of the user.

In some embodiments, the shortwave-pass filter may include a pluralityof dielectric layers, a diffractive optical element, or a reflectivematerial layer. In some embodiments, each window of the plurality ofwindows may be characterized by a diameter equal to or less than 200 μm.

In some embodiments, the eye-tracking system may also include a secondshortwave-pass filter on a second surface of the substrate opposite tothe first surface. The second shortwave-pass filter may include regionsconfigured to transmit visible light and reflect infrared light, and mayinclude a set of windows configured to transmit both visible light andinfrared light. A total area of the plurality of windows of theshortwave-pass filter on the first surface of the substrate may begreater than a total area of the set of windows of the secondshortwave-pass filter on the second surface of the substrate. In someembodiments, the eye-tracking system may also include an antireflectivelayer on a second surface of the substrate opposite to the first surfaceor on the shortwave-pass filter. In some embodiments, the eye-trackingsystem may also include a light source configured to illuminate the eyeof the user, and a control circuit configured to turn off the lightsource upon determining that a light intensity of the ambient light isgreater than a threshold value.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment including a near-eye display system accordingto certain embodiments.

FIG. 2 is a perspective view of an example of a near-eye display systemin the form of a head-mounted display (HMD) device for implementing someof the examples disclosed herein.

FIG. 3 is a perspective view of a simplified example of a near-eyedisplay system in the form of a pair of glasses for implementing some ofthe examples disclosed herein.

FIG. 4 illustrates an example of an optical see-through augmentedreality system using a waveguide display according to certainembodiments.

FIG. 5 illustrates light reflections and scattering by an eye during eyetracking.

FIG. 6 is a simplified flow chart illustrating an example method fortracking the eye of a user of a near-eye display system according tocertain embodiments.

FIG. 7A illustrates an example of an image of a user's eye captured by acamera according to certain embodiments. FIG. 7B illustrates an exampleof an identified iris region, an example of an identified pupil region,and examples of glint regions identified in an image of the user's eyeaccording to certain embodiments.

FIG. 8 illustrates an example of an eye illumination system for eyetracking according to certain embodiments.

FIG. 9 illustrates an example of an eye illumination system for eyetracking in a near-eye display system according to certain embodiments.

FIG. 10 is a front view of an example of an eye illumination systemincluding a shortwave-pass (SWP) filter having an array of windows foreye tracking in a near-eye display system according to certainembodiments.

FIG. 11A illustrates an example of an eye illumination system includinga shortwave-pass filter having an array of windows for eye-tracking in anear-eye display system according to certain embodiments.

FIG. 11B illustrates an example of ambient light passing through thearray of windows shown in FIG. 11A and reaching an eyebox according tocertain embodiments.

FIG. 11C illustrates a simulated image captured at a location behind theshortwave-pass filter according to certain embodiments.

FIG. 11D illustrates a simulated image captured at a certain distancebehind the shortwave-pass filter as illustrated in FIG. 11B according tocertain embodiments.

FIG. 12 shows example spectrum of extraterrestrial irradiance, wherelight within a spectral range in the spectrum can be used for eyetracking according to certain embodiments.

FIG. 13 illustrates example infrared spectrum of diffused ambient lightthat can be detected by a silicon-based camera according to certainembodiments.

FIG. 14 illustrates example infrared spectrum of diffused ambient lightthat can be detected by an InGaAs-based camera according to someembodiments.

FIG. 15 illustrates an example of an eye illumination system for eyetracking in a near-eye display system according to certain embodiments.

FIG. 16 is a simplified flow chart illustrating an example of a methodof manufacturing an ambient light eye illuminator according to certainembodiments.

FIG. 17 is a simplified block diagram of an example of an electronicsystem of a near-eye display system according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Techniques disclosed herein relate generally to an artificial realitysystem, and more specifically, to an eye tracking subsystem for theartificial reality system. In one embodiment, infrared (IR) light (e.g.,with wavelengths between about 750-2500 nm) in the ambient light isspatially sampled and used as light sources to illuminate the user'seyes for eye tracking.

In an artificial reality system, such as a virtual reality (VR),augmented reality (AR), or mixed reality (MR) system, to improve userinteraction with presented content, the artificial reality system maytrack the user's eye and modify or generate content based on a locationor a direction in which the user is looking at. Tracking the eye mayinclude tracking the position and/or shape of the pupil and/or thecornea of the eye, and determining the rotational position or gazedirection of the eye. To track the eye, an eye-tracking system of thenear-eye display system may include an illumination subsystem that canilluminate the user's eye using light sources mounted to or inside theartificial reality system. The eye-tracking system may also include animaging subsystem that includes an imaging device (e.g., a camera) forcapturing light reflected by various surfaces of the user's eye. Lightthat is diffusively reflected (e.g., scattered) by, for example, theiris of the user's eye may affect the contrast of the captured image inthe iris or pupil region, which may be used to determine the edges ofthe iris or pupil and the center of the pupil. Light that is reflectedspecularly off the cornea of the user's eye may result in “glints” inthe captured image. The glints may also be referred to as the firstPurkinje images or corneal reflections. Techniques such as centroidingalgorithms may be used to determine the locations of the glints on theeye in the captured image. For example, the centroiding algorithm maydetermine the center of the glint by finding the pixel location with themost energy in a local neighborhood. The rotational position (e.g., thegaze direction) of the eye may then be determined based on the locationsof the glints relative to a known feature of the eye (e.g., the centerof the pupil) within the captured image.

Existing eye-tracking systems may use light sources (e.g., infraredLEDs) positioned at the periphery of the user's field of view toilluminate the eye. The peripheral location of the light sources maynegatively impact the accuracy of eye tracking due to, for example, theangles of the illuminating light from the light sources to the eye orthe angle of the light reflected from the eye. For example, depending onthe placement of the camera (which may not be very flexible due tocertain space constraints on the artificial reality system), light froma light source at a particular point may not reach the user's eye or maynot reach the camera after being reflected by the cornea. While a largernumber of light sources in the periphery of the user's field of view mayhelp to increase the accuracy of eye tracking, increasing the number oflight sources likely would cause a large amount of power consumption,which may not be desired especially for devices designed for extendeduse.

In-field illumination may offer greater eye tracking accuracy. Forexample, the probability of capturing glints off the cornea over allgaze angles of the eye is higher when the light sources are locatedwithin the field of the user. However, in-field illumination may haveseveral challenges. For example, the light sources (e.g., LEDs) in thefield of view of the user may affect the see-through quality of the realworld images and the displayed images. In addition, the emission area ofan LED may be fairly large (e.g., with a diameter greater than about 200μm), and thus a light source used for eye illumination may be anextended source rather than a point source. Consequently, the glint maynot appear as a point in the captured image, and the spatial structurewithin the emission area of the light source may be captured by thecamera. The spatial structure captured in the image of the light sourcemay cause errors when determining the relative location of the glint inthe image using, for example, the centroiding algorithm. Furthermore, alarge number of light sources may consume a large amount of power,whereas in an artificial reality system (e.g., a head-mounted device),the total power may be limited but it is generally desirable that theartificial reality system can be used for an extended period of time.Other challenges of in-field illumination may include light safety,robustness, and the like.

According to certain embodiments of the eye illumination systemdisclosed herein, a shortwave-pass (SWP) filter with an array of windows(which can allow the IR light to pass through) may be placed in front ofthe user's eye, such as on a waveguide-based display that may be placedabout 10-20 mm in front of the user's eye. The SWP filter may allowvisible light in the ambient light to pass through at any area of thefilter and only allow IR light in the ambient light to pass through thearray of windows. As such, each window may transmit the IR light in theambient light to illuminate the user's eye, and thus may act as a pointIR light source. In this way, the array of windows in the SWP filter mayfunction as an array of IR point sources for illuminating the user'seye. In some embodiments, the SWP filter may include a hot mirrordeposited on the surface of a substrate or embedded in a substrate. Insome embodiments, the eye illumination system may also include one ormore light sources for eye illumination, where the one or more lightsources may only be turned on when the ambient light is not strongenough for eye illumination.

In this way, no internal power may be consumed to provide theillumination light when ambient light is strong, and thus theeye-tracking system may consume much less power and may be moreefficient. In addition, because no internal power is consumed to providethe illumination light, an arbitrary large number of light sources canbe provided by the SWP filter such that a large number of glints may becaptured in the image of the user's eye to increase the accuracy of eyetracking.

As used herein, visible light may refer to light with a wavelengthbetween about 380 nm to about 750 nm. Near infrared (NIR) light mayrefer to light with a wavelength between about 750 nm to about 2500 nm.The desired infrared (IR) wavelength range may refer to the wavelengthrange of IR light that can be detected by a suitable IR sensor (e.g., acomplementary metal-oxide semiconductor (CMOS), a charge-coupled device(CCD) sensor, or an InGaAs sensor), such as between 830 nm and 860 nm,between 930 nm and 980 nm, or between about 750 nm to about 1000 nm.

As also used herein, a hot mirror coating may refer to an opticalcoating through which the visible light may be transmitted substantiallyunaffected, whereas the near infrared light or infrared light may bereflected. A hot mirror may refer to a specialized dichromatic beamsplitter (also referred to as dichroic mirror) that may reflect infraredlight, while allowing visible light to pass through. Hot mirrors may bedesigned to be inserted into an optical system at an incidence anglevarying between, for example, zero and about 45 degrees, and may beuseful in a variety of applications, such as applications where thebuildup of heat can damage components or adversely affect spectralcharacteristics of the illumination source. Wavelengths of light thatmay be reflected by an infrared hot mirror may range from, for example,about 750 nm to about 2500 nm or longer.

As also used herein, a substrate may refer to a medium within whichlight may propagate. The substrate may include one or more types ofdielectric materials, such as glass, quartz, plastic, polymer,poly(methyl methacrylate) (PMMA), crystal, or ceramic. At least one typeof material of the substrate may be transparent to visible light and NIRlight. A thickness of the substrate may range from, for example, lessthan about 1 mm to about 10 mm or more. As used herein, a material maybe “transparent” to a light beam if the light beam can pass through thematerial with a high transmission rate, such as larger than 60%, 75%,80%, 90%, 95%, 98%, 99%, or higher, where a small portion of the lightbeam (e.g., less than 40%, 25%, 20%, 10%, 5%, 2%, 1%, or less) may bescattered, reflected, or absorbed by the material. The transmission rate(i.e., transmissivity) may be represented by either a photopicallyweighted or an unweighted average transmission rate over a range ofwavelengths, or the lowest transmission rate over a range ofwavelengths, such as the visible wavelength range.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof. The word “example”is used herein to mean “serving as an example, instance, orillustration.” Any embodiment or design described herein as “example” isnot necessarily to be construed as preferred or advantageous over otherembodiments or designs.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment 100 including a near-eye display system 120in accordance with certain embodiments. Artificial reality systemenvironment 100 shown in FIG. 1 may include near-eye display system 120,an optional external imaging device 150, and an optional input/outputinterface 140 that may each be coupled to an optional console 110. WhileFIG. 1 shows example artificial reality system environment 100 includingone near-eye display system 120, one external imaging device 150, andone input/output interface 140, any number of these components may beincluded in artificial reality system environment 100, or any of thecomponents may be omitted. For example, there may be multiple near-eyedisplay systems 120 monitored by one or more external imaging devices150 in communication with console 110. In some configurations,artificial reality system environment 100 may not include externalimaging device 150, optional input/output interface 140, and optionalconsole 110. In alternative configurations, different or additionalcomponents may be included in artificial reality system environment 100.

Near-eye display system 120 may be a head-mounted display that presentscontent to a user. Examples of content presented by near-eye displaysystem 120 include one or more of images, videos, audios, or somecombination thereof. In some embodiments, audios may be presented via anexternal device (e.g., speakers and/or headphones) that receives audioinformation from near-eye display system 120, console 110, or both, andpresents audio data based on the audio information. Near-eye displaysystem 120 may include one or more rigid bodies, which may be rigidly ornon-rigidly coupled to each other. A rigid coupling between rigid bodiesmay cause the coupled rigid bodies to act as a single rigid entity. Anon-rigid coupling between rigid bodies may allow the rigid bodies tomove relative to each other. In various embodiments, near-eye displaysystem 120 may be implemented in any suitable form factor, including apair of glasses. Some embodiments of near-eye display system 120 arefurther described below. Additionally, in various embodiments, thefunctionality described herein may be used in a headset that combinesimages of an environment external to near-eye display system 120 andartificial reality content (e.g., computer-generated images). Therefore,near-eye display system 120 may augment images of a physical, real-worldenvironment external to near-eye display system 120 with generatedcontent (e.g., images, video, sound, etc.) to present an augmentedreality to a user.

In various embodiments, near-eye display system 120 may include one ormore of display electronics 122, display optics 124, and an eye-trackingsystem 130. In some embodiments, near-eye display system 120 may alsoinclude one or more locators 126, one or more position sensors 128, andan inertial measurement unit (IMU) 132. Near-eye display system 120 mayomit any of these elements or include additional elements in variousembodiments. Additionally, in some embodiments, near-eye display system120 may include elements combining the function of various elementsdescribed in conjunction with FIG. 1.

Display electronics 122 may display or facilitate the display of imagesto the user according to data received from, for example, console 110.In various embodiments, display electronics 122 may include one or moredisplay panels, such as a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, an inorganic light emitting diode (ILED)display, a micro light emitting diode (mLED) display, an active-matrixOLED display (AMOLED), a transparent OLED display (TOLED), or some otherdisplay. For example, in one implementation of near-eye display system120, display electronics 122 may include a front TOLED panel, a reardisplay panel, and an optical component (e.g., an attenuator, polarizer,or diffractive or spectral film) between the front and rear displaypanels. Display electronics 122 may include pixels to emit light of apredominant color such as red, green, blue, white, or yellow. In someimplementations, display electronics 122 may display a three-dimensional(3D) image through stereo effects produced by two-dimensional panels tocreate a subjective perception of image depth. For example, displayelectronics 122 may include a left display and a right displaypositioned in front of a user's left eye and right eye, respectively.The left and right displays may present copies of an image shiftedhorizontally relative to each other to create a stereoscopic effect(i.e., a perception of image depth by a user viewing the image).

In certain embodiments, display optics 124 may display image contentoptically (e.g., using optical waveguides and couplers), magnify imagelight received from display electronics 122, correct optical errorsassociated with the image light, and present the corrected image lightto a user of near-eye display system 120. In various embodiments,display optics 124 may include one or more optical elements, such as,for example, a substrate, optical waveguides, an aperture, a Fresnellens, a convex lens, a concave lens, a filter, input/output couplers, orany other suitable optical elements that may affect image light emittedfrom display electronics 122. Display optics 124 may include acombination of different optical elements as well as mechanicalcouplings to maintain relative spacing and orientation of the opticalelements in the combination. One or more optical elements in displayoptics 124 may have an optical coating, such as an anti-reflectivecoating, a reflective coating, a filtering coating, or a combination ofdifferent optical coatings.

Magnification of the image light by display optics 124 may allow displayelectronics 122 to be physically smaller, weigh less, and consume lesspower than larger displays. Additionally, magnification may increase afield of view of the displayed content. The amount of magnification ofimage light by display optics 124 may be changed by adjusting, adding,or removing optical elements from display optics 124. In someembodiments, display optics 124 may project displayed images to one ormore image planes that may be further away from the user's eyes thannear-eye display system 120/

Display optics 124 may also be designed to correct one or more types ofoptical errors, such as two-dimensional optical errors,three-dimensional optical errors, or a combination thereof.Two-dimensional errors may include optical aberrations that occur in twodimensions. Example types of two-dimensional errors may include barreldistortion, pincushion distortion, longitudinal chromatic aberration,and transverse chromatic aberration. Three-dimensional errors mayinclude optical errors that occur in three dimensions. Example types ofthree-dimensional errors may include spherical aberration, comaticaberration, field curvature, and astigmatism.

Locators 126 may be objects located in specific positions on near-eyedisplay system 120 relative to one another and relative to a referencepoint on near-eye display system 120. In some implementations, console110 may identify locators 126 in images captured by external imagingdevice 150 to determine the artificial reality headset's position,orientation, or both. A locator 126 may be a light emitting diode (LED),a corner cube reflector, a reflective marker, a type of light sourcethat contrasts with an environment in which near-eye display system 120operates, or some combinations thereof. In embodiments where locators126 are active components (e.g., LEDs or other types of light emittingdevices), locators 126 may emit light in the visible band (e.g., about380 nm to 750 nm), in the infrared (IR) band (e.g., about 750 nm to 1mm), in the ultraviolet band (e.g., about 10 nm to about 380 nm), inanother portion of the electromagnetic spectrum, or in any combinationof portions of the electromagnetic spectrum.

External imaging device 150 may generate slow calibration data based oncalibration parameters received from console 110. Slow calibration datamay include one or more images showing observed positions of locators126 that are detectable by external imaging device 150. External imagingdevice 150 may include one or more cameras, one or more video cameras,any other device capable of capturing images including one or more oflocators 126, or some combinations thereof. Additionally, externalimaging device 150 may include one or more filters (e.g., to increasesignal to noise ratio). External imaging device 150 may be configured todetect light emitted or reflected from locators 126 in a field of viewof external imaging device 150. In embodiments where locators 126include passive elements (e.g., retroreflectors), external imagingdevice 150 may include a light source that illuminates some or all oflocators 126, which may retro-reflect the light to the light source inexternal imaging device 150. Slow calibration data may be communicatedfrom external imaging device 150 to console 110, and external imagingdevice 150 may receive one or more calibration parameters from console110 to adjust one or more imaging parameters (e.g., focal length, focus,frame rate, sensor temperature, shutter speed, aperture, etc.).

Position sensors 128 may generate one or more measurement signals inresponse to motion of near-eye display system 120. Examples of positionsensors 128 may include accelerometers, gyroscopes, magnetometers, othermotion-detecting or error-correcting sensors, or some combinationsthereof. For example, in some embodiments, position sensors 128 mayinclude multiple accelerometers to measure translational motion (e.g.,forward/back, up/down, or left/right) and multiple gyroscopes to measurerotational motion (e.g., pitch, yaw, or roll). In some embodiments,various position sensors may be oriented orthogonally to each other.

IMU 132 may be an electronic device that generates fast calibration databased on measurement signals received from one or more of positionsensors 128. Position sensors 128 may be located external to IMU 132,internal to IMU 132, or some combination thereof. Based on the one ormore measurement signals from one or more position sensors 128, IMU 132may generate fast calibration data indicating an estimated position ofnear-eye display system 120 relative to an initial position of near-eyedisplay system 120. For example, IMU 132 may integrate measurementsignals received from accelerometers over time to estimate a velocityvector and integrate the velocity vector over time to determine anestimated position of a reference point on near-eye display system 120.Alternatively, IMU 132 may provide the sampled measurement signals toconsole 110, which may determine the fast calibration data. While thereference point may generally be defined as a point in space, in variousembodiments, the reference point may also be defined as a point withinnear-eye display system 120 (e.g., a center of IMU 132).

Eye-tracking system 130 may include one or more eye-tracking systems.Eye tracking may refer to determining an eye's position, includingorientation and location of the eye, relative to near-eye display system120. An eye-tracking system may include an imaging system to image oneor more eyes and may generally include a light emitter, which maygenerate light that is directed to an eye such that light reflected bythe eye may be captured by the imaging system. For example, eye-trackingsystem 130 may include a non-coherent or coherent light source (e.g., alaser diode) emitting light in the visible spectrum or infraredspectrum, and a camera capturing the light reflected by the user's eye.As another example, eye-tracking system 130 may capture reflected radiowaves emitted by a miniature radar unit. Eye-tracking system 130 may uselow-power light emitters that emit light at frequencies and intensitiesthat would not injure the eye or cause physical discomfort. Eye-trackingsystem 130 may be arranged to increase contrast in images of an eyecaptured by eye-tracking system 130 while reducing the overall powerconsumed by eye-tracking system 130 (e.g., reducing power consumed by alight emitter and an imaging system included in eye-tracking system130). For example, in some implementations, eye-tracking system 130 mayconsume less than 100 milliwatts of power.

In some embodiments, eye-tracking system 130 may include one lightemitter and one camera to track each of the user's eyes. Eye-trackingsystem 130 may also include different eye-tracking systems that operatetogether to provide improved eye tracking accuracy and responsiveness.For example, eye-tracking system 130 may include a fast eye-trackingsystem with a fast response time and a slow eye-tracking system with aslower response time. The fast eye-tracking system may frequentlymeasure an eye to capture data used by an eye-tracking module 118 todetermine the eye's position relative to a reference eye position. Theslow eye-tracking system may independently measure the eye to capturedata used by eye-tracking module 118 to determine the reference eyeposition without reference to a previously determined eye position. Datacaptured by the slow eye-tracking system may allow eye-tracking module118 to determine the reference eye position with greater accuracy thanthe eye's position determined from data captured by the fasteye-tracking system. In various embodiments, the slow eye-trackingsystem may provide eye-tracking data to eye-tracking module 118 at alower frequency than the fast eye-tracking system. For example, the sloweye-tracking system may operate less frequently or have a slowerresponse time to conserve power.

Eye-tracking system 130 may be configured to estimate the orientation ofthe user's eye. The orientation of the eye may correspond to thedirection of the user's gaze within near-eye display system 120. Theorientation of the user's eye may be defined as the direction of thefoveal axis, which is the axis between the fovea (an area on the retinaof the eye with the highest concentration of photoreceptors) and thecenter of the eye's pupil. In general, when a user's eyes are fixed on apoint, the foveal axes of the user's eyes intersect that point. Thepupillary axis of an eye may be defined as the axis that passes throughthe center of the pupil and is perpendicular to the corneal surface. Ingeneral, even though the pupillary axis and the foveal axis intersect atthe center of the pupil, the pupillary axis may not directly align withthe foveal axis. For example, the orientation of the foveal axis may beoffset from the pupillary axis by approximately −1° to 8° laterally andabout ±4° vertically (which may be referred to as kappa angles, whichmay vary from person to person). Because the foveal axis is definedaccording to the fovea, which is located in the back of the eye, thefoveal axis may be difficult or impossible to measure directly in someeye-tracking embodiments. Accordingly, in some embodiments, theorientation of the pupillary axis may be detected and the foveal axismay be estimated based on the detected pupillary axis.

In general, the movement of an eye corresponds not only to an angularrotation of the eye, but also to a translation of the eye, a change inthe torsion of the eye, and/or a change in the shape of the eye.Eye-tracking system 130 may also be configured to detect the translationof the eye, which may be a change in the position of the eye relative tothe eye socket. In some embodiments, the translation of the eye may notbe detected directly, but may be approximated based on a mapping from adetected angular orientation. Translation of the eye corresponding to achange in the eye's position relative to the eye-tracking system due to,for example, a shift in the position of near-eye display system 120 on auser's head, may also be detected. Eye-tracking system 130 may alsodetect the torsion of the eye and the rotation of the eye about thepupillary axis. Eye-tracking system 130 may use the detected torsion ofthe eye to estimate the orientation of the foveal axis from thepupillary axis. In some embodiments, eye-tracking system 130 may alsotrack a change in the shape of the eye, which may be approximated as askew or scaling linear transform or a twisting distortion (e.g., due totorsional deformation). In some embodiments, eye-tracking system 130 mayestimate the foveal axis based on some combinations of the angularorientation of the pupillary axis, the translation of the eye, thetorsion of the eye, and the current shape of the eye.

In some embodiments, eye-tracking system 130 may include multipleemitters or at least one emitter that can project a structured lightpattern on all portions or a portion of the eye. The structured lightpattern may be distorted due to the shape of the eye when viewed from anoffset angle. Eye-tracking system 130 may also include at least onecamera that may detect the distortions (if any) of the structured lightpattern projected onto the eye. The camera may be oriented on adifferent axis to the eye than the emitter. By detecting the deformationof the structured light pattern on the surface of the eye, eye-trackingsystem 130 may determine the shape of the portion of the eye beingilluminated by the structured light pattern. Therefore, the captureddistorted light pattern may be indicative of the 3D shape of theilluminated portion of the eye. The orientation of the eye may thus bederived from the 3D shape of the illuminated portion of the eye.Eye-tracking system 130 can also estimate the pupillary axis, thetranslation of the eye, the torsion of the eye, and the current shape ofthe eye based on the image of the distorted structured light patterncaptured by the camera.

Near-eye display system 120 may use the orientation of the eye to, e.g.,determine an inter-pupillary distance (IPD) of the user, determine gazedirections, introduce depth cues (e.g., blur image outside of the user'smain line of sight), collect heuristics on the user interaction in theVR media (e.g., time spent on any particular subject, object, or frameas a function of exposed stimuli), some other functions that are basedin part on the orientation of at least one of the user's eyes, or somecombination thereof. Because the orientation may be determined for botheyes of the user, eye-tracking system 130 may be able to determine wherethe user is looking. For example, determining a direction of a user'sgaze may include determining a point of convergence based on thedetermined orientations of the user's left and right eyes. A point ofconvergence may be the point where the two foveal axes of the user'seyes intersect. The direction of the user's gaze may be the direction ofa line passing through the point of convergence and the mid-pointbetween the pupils of the user's eyes.

Input/output interface 140 may be a device that allows a user to sendaction requests to console 110. An action request may be a request toperform a particular action. For example, an action request may be tostart or to end an application or to perform a particular action withinthe application. Input/output interface 140 may include one or moreinput devices. Example input devices may include a keyboard, a mouse, agame controller, a glove, a button, a touch screen, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 110. An action request received bythe input/output interface 140 may be communicated to console 110, whichmay perform an action corresponding to the requested action. In someembodiments, input/output interface 140 may provide haptic feedback tothe user in accordance with instructions received from console 110. Forexample, input/output interface 140 may provide haptic feedback when anaction request is received, or when console 110 has performed arequested action and communicates instructions to input/output interface140.

Console 110 may provide content to near-eye display system 120 forpresentation to the user in accordance with information received fromone or more of external imaging device 150, near-eye display system 120,and input/output interface 140. In the example shown in FIG. 1, console110 may include an application store 112, a headset tracking module 114,an artificial reality engine 116, and eye-tracking module 118. Someembodiments of console 110 may include different or additional modulesthan those described in conjunction with FIG. 1. Functions furtherdescribed below may be distributed among components of console 110 in adifferent manner than is described here.

In some embodiments, console 110 may include a processor and anon-transitory computer-readable storage medium storing instructionsexecutable by the processor. The processor may include multipleprocessing units executing instructions in parallel. Thecomputer-readable storage medium may be any memory, such as a hard diskdrive, a removable memory, or a solid-state drive (e.g., flash memory ordynamic random access memory (DRAM)). In various embodiments, themodules of console 110 described in conjunction with FIG. 1 may beencoded as instructions in the non-transitory computer-readable storagemedium that, when executed by the processor, cause the processor toperform the functions further described below.

Application store 112 may store one or more applications for executionby console 110. An application may include a group of instructions that,when executed by a processor, generates content for presentation to theuser. Content generated by an application may be in response to inputsreceived from the user via movement of the user's eyes or inputsreceived from the input/output interface 140. Examples of theapplications may include gaming applications, conferencing applications,video playback application, or other suitable applications.

Headset tracking module 114 may track movements of near-eye displaysystem 120 using slow calibration information from external imagingdevice 150. For example, headset tracking module 114 may determinepositions of a reference point of near-eye display system 120 usingobserved locators from the slow calibration information and a model ofnear-eye display system 120. Headset tracking module 114 may alsodetermine positions of a reference point of near-eye display system 120using position information from the fast calibration information.Additionally, in some embodiments, headset tracking module 114 may useportions of the fast calibration information, the slow calibrationinformation, or some combination thereof, to predict a future locationof near-eye display system 120. Headset tracking module 114 may providethe estimated or predicted future position of near-eye display system120 to artificial reality engine 116.

Headset tracking module 114 may calibrate the artificial reality systemenvironment 100 using one or more calibration parameters, and may adjustone or more calibration parameters to reduce errors in determining theposition of near-eye display system 120. For example, headset trackingmodule 114 may adjust the focus of external imaging device 150 to obtaina more accurate position for observed locators on near-eye displaysystem 120. Moreover, calibration performed by headset tracking module114 may also account for information received from IMU 132.Additionally, if tracking of near-eye display system 120 is lost (e.g.,external imaging device 150 loses line of sight of at least a thresholdnumber of locators 126), headset tracking module 114 may re-calibratesome or all of the calibration parameters.

Artificial reality engine 116 may execute applications within artificialreality system environment 100 and receive position information ofnear-eye display system 120, acceleration information of near-eyedisplay system 120, velocity information of near-eye display system 120,predicted future positions of near-eye display system 120, or somecombination thereof from headset tracking module 114. Artificial realityengine 116 may also receive estimated eye position and orientationinformation from eye-tracking module 118. Based on the receivedinformation, artificial reality engine 116 may determine content toprovide to near-eye display system 120 for presentation to the user. Forexample, if the received information indicates that the user has lookedto the left, artificial reality engine 116 may generate content fornear-eye display system 120 that reflects the user's eye movement in avirtual environment. Additionally, artificial reality engine 116 mayperform an action within an application executing on console 110 inresponse to an action request received from input/output interface 140,and provide feedback to the user indicating that the action has beenperformed. The feedback may be visual or audible feedback via near-eyedisplay system 120 or haptic feedback via input/output interface 140.

Eye-tracking module 118 may receive eye-tracking data from eye-trackingsystem 130 and determine the position of the user's eye based on theeye-tracking data. The position of the eye may include an eye'sorientation, location, or both relative to near-eye display system 120or any element thereof. Because the eye's axes of rotation change as afunction of the eye's location in its socket, determining the eye'slocation in its socket may allow eye-tracking module 118 to moreaccurately determine the eye's orientation.

In some embodiments, eye-tracking module 118 may store a mapping betweenimages captured by eye-tracking system 130 and eye positions todetermine a reference eye position from an image captured byeye-tracking system 130. Alternatively or additionally, eye-trackingmodule 118 may determine an updated eye position relative to a referenceeye position by comparing an image from which the reference eye positionis determined to an image from which the updated eye position is to bedetermined. Eye-tracking module 118 may determine eye position usingmeasurements from different imaging devices or other sensors. Forexample, eye-tracking module 118 may use measurements from a sloweye-tracking system to determine a reference eye position, and thendetermine updated positions relative to the reference eye position froma fast eye-tracking system until a next reference eye position isdetermined based on measurements from the slow eye-tracking system.

Eye-tracking module 118 may also determine eye calibration parameters toimprove precision and accuracy of eye tracking. Eye calibrationparameters may include parameters that may change whenever a user donsor adjusts near-eye display system 120. Example eye calibrationparameters may include an estimated distance between a component ofeye-tracking system 130 and one or more parts of the eye, such as theeye's center, pupil, cornea boundary, or a point on the surface of theeye. Other example eye calibration parameters may be specific to aparticular user and may include an estimated average eye radius, anaverage corneal radius, an average sclera radius, a map of features onthe eye surface, and an estimated eye surface contour. In embodimentswhere light from the outside of near-eye display system 120 may reachthe eye (as in some augmented reality applications), the calibrationparameters may include correction factors for intensity and colorbalance due to variations in light from the outside of near-eye displaysystem 120. Eye-tracking module 118 may use eye calibration parametersto determine whether the measurements captured by eye-tracking system130 would allow eye-tracking module 118 to determine an accurate eyeposition (also referred to herein as “valid measurements”). Invalidmeasurements, from which eye-tracking module 118 may not be able todetermine an accurate eye position, may be caused by the user blinking,adjusting the headset, or removing the headset, and/or may be caused bynear-eye display system 120 experiencing greater than a threshold changein illumination due to external light. In some embodiments, at leastsome of the functions of eye-tracking module 118 may be performed byeye-tracking system 130.

FIG. 2 is a perspective view of an example of a near-eye display systemin the form of a head-mounted display (HMD) device 200 for implementingsome of the examples disclosed herein. HMD device 200 may be a part of,e.g., a virtual reality (VR) system, an augmented reality (AR) system, amixed reality (MR) system, or some combinations thereof. HMD device 200may include a body 220 and a head strap 230. FIG. 2 shows a top side223, a front side 225, and a right side 227 of body 220 in theperspective view. Head strap 230 may have an adjustable or extendiblelength. There may be a sufficient space between body 220 and head strap230 of HMD device 200 for allowing a user to mount HMD device 200 ontothe user's head. In various embodiments, HMD device 200 may includeadditional, fewer, or different components. For example, in someembodiments, HMD device 200 may include eyeglass temples and templestips as shown in, for example, FIG. 2, rather than head strap 230.

HMD device 200 may present to a user media including virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements. Examples of the media presented by HMDdevice 200 may include images (e.g., two-dimensional (2D) orthree-dimensional (3D) images), videos (e.g., 2D or 3D videos), audios,or some combinations thereof. The images and videos may be presented toeach eye of the user by one or more display assemblies (not shown inFIG. 2) enclosed in body 220 of HMD device 200. In various embodiments,the one or more display assemblies may include a single electronicdisplay panel or multiple electronic display panels (e.g., one displaypanel for each eye of the user). Examples of the electronic displaypanel(s) may include, for example, a liquid crystal display (LCD), anorganic light emitting diode (OLED) display, an inorganic light emittingdiode (ILED) display, a micro light emitting diode (mLED) display, anactive-matrix organic light emitting diode (AMOLED) display, atransparent organic light emitting diode (TOLED) display, some otherdisplay, or some combinations thereof. HMD device 200 may include twoeye box regions.

In some implementations, HMD device 200 may include various sensors (notshown), such as depth sensors, motion sensors, position sensors, andeye-tracking sensors. Some of these sensors may use a structured lightpattern for sensing. In some implementations, HMD device 200 may includean input/output interface for communicating with a console. In someimplementations, HMD device 200 may include a virtual reality engine(not shown) that can execute applications within HMD device 200 andreceive depth information, position information, accelerationinformation, velocity information, predicted future positions, or somecombination thereof of HMD device 200 from the various sensors. In someimplementations, the information received by the virtual reality enginemay be used for producing a signal (e.g., display instructions) to theone or more display assemblies. In some implementations, HMD device 200may include locators (not shown, such as locators 126) located in fixedpositions on body 220 relative to one another and relative to areference point. Each of the locators may emit light that is detectableby an external imaging device.

FIG. 3 is a perspective view of a simplified example near-eye displaysystem 300 in the form of a pair of glasses for implementing some of theexamples disclosed herein. Near-eye display system 300 may be a specificimplementation of near-eye display system 120 of FIG. 1, and may beconfigured to operate as a virtual reality display, an augmented realitydisplay, and/or a mixed reality display. Near-eye display system 300 mayinclude a frame 305 and a display 310. Display 310 may be configured topresent content to a user. In some embodiments, display 310 may includedisplay electronics and/or display optics. For example, as describedabove with respect to near-eye display system 120 of FIG. 1, display 310may include an LCD display panel, an LED display panel, or an opticaldisplay panel (e.g., a waveguide display assembly).

Near-eye display system 300 may further include various sensors 350 a,350 b, 350 c, 350 d, and 350 e on or within frame 305. In someembodiments, sensors 350 a-350 e may include one or more depth sensors,motion sensors, position sensors, inertial sensors, or ambient lightsensors. In some embodiments, sensors 350 a-350 e may include one ormore image sensors configured to generate image data representingdifferent fields of views in different directions. In some embodiments,sensors 350 a-350 e may be used as input devices to control or influencethe displayed content of near-eye display system 300, and/or to providean interactive VR/AR/MR experience to a user of near-eye display system300. In some embodiments, sensors 350 a-350 e may also be used forstereoscopic imaging.

In some embodiments, near-eye display system 300 may further include oneor more illuminators 330 to project light into the physical environment.The projected light may be associated with different frequency bands(e.g., visible light, infra-red light, ultra-violet light, etc.), andmay serve various purposes. For example, illuminator(s) 330 may projectlight in a dark environment (or in an environment with low intensity ofinfra-red light, ultra-violet light, etc.) to assist sensors 350 a-350 ein capturing images of different objects within the dark environment. Insome embodiments, illuminator(s) 330 may be used to project certainlight pattern onto the objects within the environment. In someembodiments, illuminator(s) 330 may be used as locators, such aslocators 126 described above with respect to FIG. 1.

In some embodiments, near-eye display system 300 may also include ahigh-resolution camera 340. Camera 340 may capture images of thephysical environment in the field of view. The captured images may beprocessed, for example, by a virtual reality engine (e.g., artificialreality engine 116 of FIG. 1) to add virtual objects to the capturedimages or modify physical objects in the captured images, and theprocessed images may be displayed to the user by display 310 for AR orMR applications.

FIG. 4 illustrates an example of an optical see-through augmentedreality system 400 using a waveguide display according to certainembodiments. Augmented reality system 400 may include a projector 410and a combiner 415. Projector 410 may include a light source or imagesource 412 and projector optics 414. In some embodiments, image source412 may include a plurality of pixels that displays virtual objects,such as an LCD display panel or an LED display panel. In someembodiments, image source 412 may include a light source that generatescoherent or partially coherent light. For example, image source 412 mayinclude a laser diode, a vertical cavity surface emitting laser, and/ora light emitting diode. In some embodiments, image source 412 mayinclude a plurality of light sources each emitting a monochromatic imagelight corresponding to a primary color (e.g., red, green, or blue). Insome embodiments, image source 412 may include an optical patterngenerator, such as a spatial light modulator. Projector optics 414 mayinclude one or more optical components that can condition the light fromimage source 412, such as expanding, collimating, scanning, orprojecting light from image source 412 to combiner 415. The one or moreoptical components may include, for example, one or more lenses, liquidlenses, mirrors, apertures, and/or gratings. In some embodiments,projector optics 414 may include a liquid lens (e.g., a liquid crystallens) with a plurality of electrodes that allows scanning of the lightfrom image source 412.

Combiner 415 may include an input coupler 430 for coupling light fromprojector 410 into a substrate 420 of combiner 415. Combiner 415 maytransmit at least 50% of light in a first wavelength range and reflectat least 25% of light in a second wavelength range. For example, thefirst wavelength range may be visible light from about 400 nm to about650 nm, and the second wavelength range may be in the infrared band, forexample, from about 800 nm to about 1000 nm. Input coupler 430 mayinclude a volume holographic grating, a diffractive optical elements(DOE) (e.g., a surface-relief grating), a slanted surface of substrate420, or a refractive coupler (e.g., a wedge or a prism). Input coupler430 may have a coupling efficiency of greater than 30%, 50%, 75%, 90%,or higher for visible light. Light coupled into substrate 420 maypropagate within substrate 420 through, for example, total internalreflection (TIR). Substrate 420 may be in the form of a lens of a pairof eyeglasses. Substrate 420 may have a flat or a curved surface, andmay include one or more types of dielectric materials, such as glass,quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, orceramic. A thickness of the substrate may range from, for example, lessthan about 1 mm to about 10 mm or more. Substrate 420 may be transparentto visible light.

Substrate 420 may include or may be coupled to a plurality of outputcouplers 440 configured to extract at least a portion of the lightguided by and propagating within substrate 420 from substrate 420, anddirect extracted light 460 to an eye 490 of the user of augmentedreality system 400. As input coupler 430, output couplers 440 mayinclude grating couplers (e.g., volume holographic gratings orsurface-relief gratings), other DOEs, prisms, etc. Output couplers 440may have different coupling (e.g., diffraction) efficiencies atdifferent locations. Substrate 420 may also allow light 450 fromenvironment in front of combiner 415 to pass through with little or noloss. Output couplers 440 may also allow light 450 to pass through withlittle loss. For example, in some implementations, output couplers 440may have a low diffraction efficiency for light 450 such that light 450may be refracted or otherwise pass through output couplers 440 withlittle loss, and thus may have a higher intensity than extracted light460. In some implementations, output couplers 440 may have a highdiffraction efficiency for light 450 and may diffract light 450 tocertain desired directions (i.e., diffraction angles) with little loss.As a result, the user may be able to view combined images of theenvironment in front of combiner 415 and virtual objects projected byprojector 410.

There may be several types of eye measurements for determining userintent, cognitive processes, behavior, attention, etc. Thesemeasurements may include, for example, measurement related to fixations,where the eyes are stationary between movements and visual input mayoccur. Fixation-related measurement variables may include, for example,total fixation duration, mean fixation duration, fixation spatialdensity, number of areas fixated, fixation sequences, and fixation rate.The eye measurements may also include measurements of saccades, whichare rapid eye movements that occur between fixations. Saccade relatedparameters may include, for example, saccade number, amplitude,velocity, acceleration, and fixation-saccade ratio. The eye measurementsmay also include measurements of scanpath, which may include a series ofshort fixations and saccades alternating before the eyes reach a targetlocation on the display screen. Movement measures derived from scanpathmay include, for example, scanpath direction, duration, length, and areacovered. The eye movement measurements may further include measuring thesum of all fixations made in an area of interest before the eyes leavethat area or the proportion of time spent in each area. The eyemeasurements may also include measuring pupil size and blink rate, whichmay be used to study cognitive workload.

In addition, as described above, in an artificial reality system, toimprove user interaction with presented content, the artificial realitysystem may track the user's eye and modify or generate content based ona location or a direction in which the user is looking at. Tracking theeye may include tracking the position and/or shape of the pupil and/orthe cornea of the eye, and determining the rotational position or gazedirection of the eye. One technique (referred to as Pupil Center CornealReflection or PCCR method) involves using NIR LEDs to produce glints onthe eye cornea surface and then capturing images/videos of the eyeregion. Gaze direction can be estimated from the relative movementbetween the pupil center and glints.

FIG. 5 illustrates light reflections and scattering by an eye 550 duringeye tracking using an eye-tracking system 510, such as eye-trackingsystem 130. Eye-tracking system 510 may include a light source 512 and acamera 514 as described above. In other embodiments, eye-tracking system510 may include different and/or additional components than thosedepicted in FIG. 5. Light source 512 may include, for example, a laser,an LED, or VCSELs, and may be mounted at a laser angle 522 relative to asurface normal vector 520 of eye 550. Surface normal vector 520 isorthogonal to a portion of the surface (e.g., cornea 552) of eye 550illuminated by light source 512. In the example shown in FIG. 5, surfacenormal vector 520 may be the same as the pupillary axis (also referredto as optical axis, which may be a line passing through the center ofpupil 556 and the center of cornea 552) of eye 550. Laser angle 522 maybe measured between surface normal vector 520 and a line from a centerof the portion of the surface of eye 550 illuminated by light source 512to a center of the output aperture of light source 512. Camera 514 maybe mounted at a camera angle 524 relative to surface normal vector 520of eye 550. Camera angle 524 may be measured between surface normalvector 520 and a line from a center of the portion of the surface of eye550 illuminated by light source 512 to a center of the image sensor orlight input aperture of camera 514. In some embodiments, a differencebetween laser angle 522 and camera angle 524 is less than a thresholdamount so that camera 514 may capture images via specular reflections oflight incident on cornea 552 of eye 550, which may beneficially increasecontrast of the resulting image and minimize light power loss and powerconsumption.

The light emitted by light source 512 may substantially uniformlyilluminate a portion of the eye surface (e.g., cornea 552). A portion ofthe emitted light may be reflected specularly by cornea 552 of eye 550and captured by camera 514. In some cases, the light incident on eye 550may propagate into the eye for a small distance before being reflected.For example, at least some portions of the light may enter eye 550through cornea 552 and reach iris 554, pupil 556, lens 558, or retina560 of eye 550. Because some interfaces within eye 550 (e.g., surface ofiris 554) may be rough (e.g., due to features such as capillaries orbumps), the interfaces within eye 550 may scatter the incident light inmultiple directions. Different portions of the eye surface and theinterfaces within eye 550 may have different patterns of features. Thus,an intensity pattern of the light reflected by eye 550 may depend on thepattern of features within the illuminated portion of eye 550, which mayallow identification of the portions of the eye (e.g., iris 554 or pupil556) from the intensity pattern.

Camera 514 may collect and project light reflected by the illuminatedportion of eye 550 onto an image sensor of camera 514. Camera 514 mayalso correct one or more optical errors (such as those described withrespect to the display optics 124) to improve the contrast and otherproperties of the images captured by the image sensor of camera 514. Insome embodiments, camera 514 may also magnify the reflected light. Insome embodiments, camera 514 may enlarge the images. The image sensor ofcamera 514 may capture incident light focused by a lens assembly ofcamera 514. Thus, camera 514 may effectively capture an image of lightsource 512 (the emitted light of which is reflected specularly by thecornea of the eye) reflected by the eye, resulting in a “glint” in thecaptured image. Because of the scattering (diffusive reflections) atsome interfaces of the eye, light incident on a point of the imagesensor may include light reflected from multiple points within theilluminated portion of eye 550, and thus may be the result of theinterference of the light reflected from the multiple points. Thus, insome embodiments, the image sensor of camera 514 may also capture adiffraction or speckle pattern formed by a combination of lightreflected from multiple points of the surface of eye 550.

Each pixel of the image sensor may include a light-sensitive circuitthat can output a current or voltage signal corresponding to theintensity of the light incident on the pixel. In some embodiments, thepixels of the image sensor may be sensitive to light in a narrowwavelength band. In some other embodiments, the pixels of the imagesensor may have a wide-band or multi-band sensitivity. For example, theimage sensor of camera 514 may include a complementary metal-oxidesemiconductor (CMOS) pixel array, which may be used with light having awavelength less than about 750 nm. As another example, the image sensorof camera 514 may include an indium gallium arsenide (InGaAs) alloypixel array or a charge-coupled device (CCD). Such an image sensor maybe used with a laser emitting light having a wavelength between about900 nm and about 1160 nm.

In some embodiments, to determine a position change of eye 550, aneye-tracking module (e.g., eye-tracking system 130 or eye-trackingmodule 118 of FIG. 1) may determine a pixel shift between images.Multiplying the pixel shift by a calibrated distance per pixel may allowthe eye-tracking module to determine a distance the surface (e.g.,cornea 552) of eye 550 has shifted. For example, if the glint capturedin one image is shifted by two pixels relative to the glint captured ina previous image, and each pixel corresponds to a distance of 10micrometers at the surface of eye 550, the surface of eye 550 may havemoved about 20 micrometers.

In some embodiments, eye-tracking techniques used in head-mounteddevices may be video-based and may be performed based on appearance orfeatures. For example, the appearance-based techniques may use certainmapping functions to map the entire eye image or a region of interest ofthe eye image to a gaze direction or point-of-gaze. The mapping functionmay have a high-dimensional input (e.g., the intensities of imagepixels) and a low-dimensional output (e.g., the gaze direction,point-of-gaze, etc.). These mapping functions may be based on machinelearning models, such as convolutional neural networks (CNNs).

The feature-based techniques may perform feature extraction and gazeestimation using the extracted features. The features can be any one ormore of the following: pupil center, iris center, pupil-iris boundary,iris-sclera boundary, first Purkinje images (reflections off the frontsurface of the cornea, known as corneal reflections or glints), fourthPurkinje images (reflections of the back surface of the crystallinelens), eye corners, and the like. These features may be extracted usingcomputer vision techniques (e.g., intensity histogram analysis,thresholding, edge detection, blob segmentation, convex-hull,morphological operations, shape fitting, deformable templates,centroiding, etc.) or machine-learning techniques, or any combination.The gaze estimation techniques can be interpolation-based ormodel-based. The interpolation-based techniques may use certain mappingfunctions (e.g., second degree bivariate polynomial) to map eye features(e.g., pupil center or pupil center-corneal reflection (PCCR) vector) tothe gaze direction. The coefficients of these mapping functions may beobtained through a personal calibration procedure that may involvecollecting data while the user fixates at a sequence of fixation targetswith known coordinates. This calibration may be performed for eachsubject and each session, and may sometimes be performed multiple timesin each session, because the calibration may be sensitive to slippage ofthe head-mounted device relative to the head. The mapping functions maythen use the calibration data points and interpolation techniques todetermine the gaze direction. The model-based methods may use models ofthe system (e.g., camera(s) and/or light source(s)) and the eye that mayinclude actual physical system parameters and anatomical eye parametersto determine a 3-D gaze from a set of eye features (e.g., pupil boundaryand multiple corneal reflections) according to 3-D geometry. Model-basedtechniques may perform both a one-time system calibration and a one-timepersonal calibration for each user. The data collection procedure forthe personal calibration may be similar to that of theinterpolation-based methods.

Alternatively or additionally, the eye-tracking module may determine theposition of the eye in a captured image by comparing the captured imageswith one or more previous images having known positions of the eye. Forexample, the eye-tracking module may include a database of images thatare each associated with a reference eye position. By matching thecaptured image with a stored image, the eye-tracking module maydetermine that the eye is at the reference eye position associated withthe stored image. In some embodiments, the eye-tracking module mayidentify a feature in a portion of a captured image. The feature mayinclude a diffraction or optical flow pattern associated with aparticular portion of eye 550, such as the pupil or the iris. Forexample, the eye-tracking module may determine the eye position byretrieving a reference eye position associated with the feature (whichwas also captured in a reference image), determining a pixel shiftbetween the feature in the captured image and the feature in thereference image, and determining the eye position based on thedetermined pixel shift with respect to the reference eye position andthe calibrated distance per pixel as described above.

As discussed above, camera 514 may effectively capture an image of lightsource 512 reflected by cornea 552 of eye 550. In some embodiments, theeye-tracking module may determine a gaze direction of the user's eyebased on the locations of the images of the light sources (e.g., glints)on cornea 552 in the captured image. The gaze direction may bedetermined by a foveal axis 526 of the user's eyes, where foveal axis526 (also referred to as “visual axis”) may be a line passing throughthe center of pupil 556 and the center of fovea 562.

FIG. 6 is a simplified flow chart 600 illustrating an example method fortracking the eye of a user of a near-eye display system according tocertain embodiments. The operations in flow chart 600 may be performedby, for example, eye-tracking system 130 or 510 described above. Atblock 610, one or more light sources may illuminate the user's eye. Invarious embodiments, the light sources may be located in the field ofview of the user's eye or at a periphery of the field of view of theuser's eye. In some embodiments, a light source may be located at theperiphery of the field of view of the user's eye, and the light from thelight source may be guided and directed to the user's eye from locationsin the field of view of the user's eye.

At block 620, an imaging device (e.g., a camera) may collect lightreflected by the user's eye and generate one or more images of theuser's eye. As described above, the cornea of the user's eye mayspecularly reflect the illumination light, while some portions of theuser's eye (e.g., iris) may diffusively scatter the illumination light.The images of the user's eye may include portions (e.g., the iris regionand/or the pupil portion) where the contrast may be different due to thescattering of the illumination light. The images of the user's eye mayalso include glints caused by the specular reflection of theillumination light by the user's cornea.

FIG. 7A illustrates an example of an image 700 of a user's eye capturedby a camera according to certain embodiments. Image 700 includes an irisregion 710, a pupil region 720, and multiple glints 730. Glints 730 maybe caused by illumination light specularly reflected off the cornea ofthe user's eye.

Optionally, at block 630, the eye-tracking system may perform systemcalibration to improve the precision and accuracy of eye tracking asdescribed above with respect to eye-tracking module 118. The systemcalibration may include, for example, calibrating the eye trackingoptical path (such as extrinsic (e.g., position or orientation) andintrinsic camera parameters), positions of the light sources, thedisplay optical path (e.g., position of the display, extrinsic andintrinsic parameters of the display optics, etc.)

At block 640, the location of the center of the pupil of the user's eyemay be determined based on the scattering of the illumination light by,for example, the iris of the user's eye. As described above, theboundaries of the pupil and/or the iris may be determined based on imagesegmentation of the pupil region in the captured image as shown in FIG.7A. Based on the boundaries of the pupil, the location of the center ofthe pupil may be determined.

At block 650, the position of the cornea of the user's eye may bedetermined based on the locations of the glints in the captured image ofthe user's eye as shown in FIG. 7A. As described above, the locations ofthe glints may be determined using, for example, a Gaussian centroidingtechnique. The accuracy and precision of the determined locations of theglints may depend on the locations of the light sources (or virtual oreffective light sources). Based on the locations of two or more glints,the position of the cornea may be determined using, for example,nonlinear optimization and based on the assumption that the cornea (inparticular, the corneal apex) is close to a sphere.

FIG. 7B illustrates an example of an identified iris region 740, anexample of an identified pupil region 750, and examples of glint regions760 identified in image 700 of the user's eye according to certainembodiments. As illustrated, edges of iris region 740 and pupil region750 are identified. The center of pupil region 720 may then bedetermined based on the edges of pupil region 750 and/or iris region740. The locations of glints 730 can also be determined based on thelocations of glint regions 760 identified in image 700. Based on thelocations of glint regions 760, the position of the center of the corneamay be determined.

Optionally, at block 660, the eye-tracking system may perform usercalibration to determine certain eye calibration parameters forimproving the precision and accuracy of eye tracking as described abovewith respect to eye-tracking module 118 and FIG. 5. The user calibrationmay include, for example, determining the eye model parameters (e.g.,anatomical eye parameters) or the coefficients of some mapping functionsthat may not depend on a particular eye parameter. Other examples of theeye calibration parameters may include an estimated average eye radius,an average corneal radius, an average sclera radius, a map of featureson the eye surface, and an estimated eye surface contour. As describedabove, a kappa angle between the pupillary axis (optical axis) and thefoveal axis (visual axis) of the use's eye may be different fordifferent users, and thus may need to be calibrated during thecalibration. In some embodiments, the calibration may be performed bydisplaying a set of target points distributed over a display screenaccording to A certain pattern, and the user is asked to gaze at each ofthe target points for a certain amount of time. The camera may capturethe corresponding eye positions for the target points, which are thenmapped to the corresponding gaze coordinates or directions, and theeye-tracking system may then learn the mapping function or the modelparameters. In some embodiments, the calibrations at block 630 and 660may only be performed once when the near-eye display system is put on ormoved.

At block 670, the gaze direction of the user's eye may be determinedbased on, for example, the location of the center of the pupil and theposition of the center of the cornea. In some embodiments, the pupillaryaxis of the use's eye may be determined first and may then be used todetermine the foveal axis (or line of sight, gaze direction, or visualaxis) of the user's eye, for example, based on an angle between thepupillary axis and the foveal axis.

In many cases, the light source may be an extended source rather than apoint source. Thus, the captured image (i.e., the glint) of light source512 may have a shape of a circle, a rectangle, an oval, or an irregularshape that resembles the shape of the light source, and the spatialstructure of light source 512 may be captured in the image. The extendedshape of the glint and/or the spatial structure captured in the image ofthe light source may cause errors when determining the relative locationof the glint in the image using, for example, the centroiding algorithm.The errors may affect the accuracy of eye tracking when the relativelocation (e.g., pixel shift) of the glints in the image is used todetermine the corneal location in 3D space.

In addition, the peripheral location of light source 512 may negativelyimpact the accuracy of the eye tracking due to, for example, the angleof the illumination light from the light source to the eye and the angleof the reflected light with respect to the camera. For example, when thegaze angle of the eye changes, the reflected light may not be directedto the camera or may be directed to the camera at an extreme angle,which may reduce the accuracy of the eye tracking. In some cases, thelight may be obstructed by facial features such as eye lids, eye lashes,etc., and thus may not be able to reach at least some portions or thewhole area of the cornea (or iris) or the camera. Thus, in manyimplementations, multiple light sources and/or multiple cameras in theperiphery of the user's field of view may be used as shown in FIG. 3 inorder to improve the accuracy of the eye tracking. For example, a ringof light sources may be placed around the circumference of displayelectronics and display optics. These light sources may illuminate theeye approximately uniformly and allow for segmentation of the pupil andthe iris of the eye. In general, the greater the number of lightsources, the better the accuracy of eye-tracking (approximatelyproportional to the square root of the number of light sources).However, it is not practical to use a large number of light sourcesbecause they may consume too much power and/or increase the bill ofmaterials.

For example, a point source array for eye illumination may have ahigh-power consumption. In one example, the power consumption of aninfrared LED may be more than 100 mW, and therefore the total power usedby an 8-LED array may be close to or more than about 1 Watt. Such a highpower consumption by the light sources of the eye-tracking system maynot be desired for an artificial reality system, such as an augmentedreality head mount device that may include a limited amount of power andis expected to operate over a long period of time. Furthermore, asdescribed above, the accuracy of estimating the eye gazing direction maydepend on the light source pattern and the number of light sources. Ingeneral, the larger the number of light sources, the more accurate theeye gazing direction tracking can be. However, it is impractical toarrange a large number of light sources in the field of view due to thelarge power consumption by the light sources.

According to certain embodiments, infrared (IR) spectrum (e.g., 750-2500nm) of the ambient light can be used to illuminate the user's eyes foreye tracking. For example, a near-eye display system may include ashortwave-pass (SWP) filter with a one-dimensional or two-dimensionalarray of windows (or apertures, which may allow the IR light to passthrough) placed in front of the user's eye. The filter may allow visiblelight in the ambient light to pass through at any area of the filter andmay only allow IR light in the ambient light to pass through the arrayof windows. Thus, each window may transmit the IR light in the ambientlight, and hence may function as a point IR light source. In this way,the SWP filter with the array of windows may function as point sourcesfor illuminating the user's eye with IR light from ambient light.

FIG. 8 illustrates an example of an eye illumination system 800 for eyetracking according to certain embodiments. Eye illumination system 800may include an ambient light illuminator 810 that may include asubstrate 820, a shortwave-pass (SWP) filter 830 on one surface ofsubstrate 820, and an antireflective (AR) coating 840 on another surfaceof substrate 820 opposite to SWP filter 830. Substrate 820 may include atransparent material as described above and may have any suitablethickness. SWP filter 830 may include a thin layer of reflective coatingthat may reflect light with wavelengths greater than a threshold value,such as IR light with wavelengths greater than 750 nm, while allowinglight with wavelengths shorter than the threshold value to pass throughwith little or no loss. AR coating 840 may be an AR coating for visiblelight or an AR coating for both visible light and IR light. In someembodiments, AR coating 840 may also be an SWP filter that may reflectIR light and transmit visible light.

An array of holes may be drilled through ambient light illuminator 810,including SWP filter 830, substrate 820, and/or AR coating 840, to forman array of windows 850 (or apertures) where IR light may pass through.In some embodiments, the array of holes may be filled with a materialthat is transparent to both IR light and visible light. Therefore, whenambient light 860 illuminates the ambient light illuminator 810, visiblelight can pass through the entire ambient light illuminator 810 withlittle or no loss, while IR light can only pass through windows 850. IRlight rays 870 pass through each window 850 may form a light bundle 880to illuminate a user's eye 890. Thus, each window 850 may function as apoint source. In some embodiments, the area of each window may be about100 um², 400 um², 1000 um², 2500 um², 10⁴ um², or larger. The window mayhave a circular, oval, rectangular, hexagonal cross-sectional shape, orthe like.

In some embodiments, SWP filter 830 may include a hot mirror that mayonly reflect light with longer wavelengths, such as greater than 750 nm.For example, the hot mirror may include multiple thin dielectric layers(i.e., thin films) of different dielectric materials and/or thicknesses.In some embodiments, the hot mirror may include a diffractive opticalelement that is transparent to visible light and reflects IR light. Forexample, the hot mirror may include one or more Fresnel lenses or ameta-grating. In some embodiments, the hot mirror may include a photoniccrystal structure that is transparent to visible light and reflects IRlight. In some embodiments, the hot mirror may be coated with a layer ofmaterial that is transparent to visible light and opaque (e.g.,absorptive) to IR light.

FIG. 9 illustrates another example of an eye illumination system 900 foreye tracking according to certain embodiments. Eye illumination system900 may include an ambient light illuminator 910 that may include asubstrate 920 and a shortwave-pass (SWP) filter 930 on one surface(e.g., the bottom surface) of substrate 920. Substrate 920 may include atransparent material as described above and may have any suitablethickness. SWP filter 930 may include a thin layer of reflective coatingthat may reflect light with wavelengths greater than a threshold value,such as IR light with wavelengths greater than 750 nm, while allowinglight with wavelengths shorter than the threshold value to pass throughwith little or no loss.

SWP filter 930 may be similar to SWP filter 830 and may include a hotmirror that only reflect light with longer wavelengths, such as greaterthan 750 nm. An array of holes or openings may be formed on SWP filter930 to form an array of windows 940 (or apertures) where IR light maypass through. Therefore, when ambient light 950 illuminates ambientlight illuminator 910, visible light in the ambient light can passthrough the entire ambient light illuminator 910 (including SWP filter930) with little or no loss, while IR light in the ambient light canonly pass through windows 940. IR light rays 960 pass through eachwindow 940 may form a light bundle 970 to illuminate a user's eye 990.Thus, each window 940 may function as a point source. In this way, noholes need to be drilled in substrate 920 and windows 940 may berelatively easily formed on SWP filter 930 using etching or lasercutting techniques.

In some embodiments, ambient light illuminator 910 may also include anantireflective coating layer 980 formed on SWP filter 930.Antireflective coating layer 980 may fill the holes or openings in SWPfilter 930 to form transparent windows in SWP filter 930, and may reducethe reflection of visible light and IR light at the interface betweenambient light illuminator 910 and air. In some embodiments, ambientlight illuminator 910 may also include another antireflective coatinglayer (not shown in FIG. 9) formed on the top surface of substrate 920to reduce reflection at the top surface of substrate 920.

FIG. 10 is a front view of an example of an eye illumination system 1000including a shortwave-pass (SWP) filter 1010 having an array of windowsfor eye tracking in a near-eye display system according to certainembodiments. FIG. 10 shows a two-dimensional array of windows 1020 thatincludes a plurality of windows 1030 arranged according to a pattern.The diameter of each window 1030 may be comparable to the light emissionarea of an LED source, such as less than about 200 μm. Each window mayfunction as an IR point source when illuminated by ambient light.Because SWP filter 1010 is transparent to visible light and the size ofeach window 1030 may be smaller than the resolution of the user's eye,windows 1030 may be invisible to the user's eye. The pattern in whichwindows 1030 are arranged can be determined based on the desiredaccuracy of eye tracking and the eye-tracking techniques used. In someembodiments, the windows may be located on the circumferences (e.g.,circumferences 1022 and 1024) of different regions (e.g., differentnested regions), where the regions may have square, circular,elliptical, or other custom-designed shapes. The number of nestedregions may be from 1 to a large number as desired for accurateeye-tracking because of the small size of each window. Windows 1030 onthe circumferences of different regions can be arranged similarly ordifferently, and may be aligned, interleaved, or unaligned.

FIG. 11A illustrates an example of an eye illumination system includinga shortwave-pass filter 1110 having an array of windows 1120 foreye-tracking in a near-eye display system according to certainembodiments. In the example shown in FIG. 11A, SWP filter 1110 includes8 windows 1120 arranged on the circumference of a square. Each windowhas a diameter of 200 μm and is spaced apart from adjacent windows byabout 9 mm.

FIG. 11B illustrates an example of ambient light passing through thearray of windows 1120 shown in FIG. 11A and reaching an eyebox accordingto certain embodiments. In the example shown in FIG. 11B, ambient IRlight may incident on SWP filter 1110, but may only be transmitted bySWP filter 1110 at windows 1120, as indicated by light rays 1130, toilluminate a square area 1140 (about 15 mm×15 mm), which may be placedabout 18 mm away from SWP filter 1110. Square area 1140 may representthe eyebox and the surrounding area.

FIG. 11C illustrates a simulated image 1160 captured at a plane 1150behind shortwave-pass filter 1110 according to certain embodiments.Image 1160 shows the distribution of IR light after SWP filter 1110. Asillustrated, at plane 1150 right after SWP filter 1110, IR light spots1152 may only be in small areas, where each area or light spot 1152 maybe about the same size as each window 1120. Thus, SWP filter 1110, whenilluminated by ambient light, may function as a set of IR point sources.

FIG. 11D illustrates a simulated image 1170 captured at a certaindistance behind shortwave-pass filter 1110 according to certainembodiments. For example, image 1170 may be captured at square area1140. As illustrated, square area 1140 may be evenly illuminated byambient IR light rays 1130 passing through the array of windows 1120.The total power of the ambient IR light illuminating the eyebox (e.g.,square area 1140) can be calculated to determine if the IR light fromambient light is strong enough for eye tracking purposes.

FIG. 12 shows example spectrum 1200 of extraterrestrial irradiance,where light within a spectral range (e.g., 750-2500 nm) in the spectrumcan be used for eye tracking according to certain embodiments. Accordingto the Simple Model of the Atmospheric Radiative Transfer of Sunshine(SMARTS) from National Renewable Energy Laboratory (NREL), the totalirradiance from the sun is about 1367 Watt/m². The usable IR spectralrange may depend on the type of IR camera used. For example, asilicon-based camera may be sensitive to light with wavelengths rangingfrom about 750 nm to about 1000 nm. The total irradiance in thewavelength range of 750 nm-1000 nm from the sun may be calculated to beabout 223.4511 Watt/m².

FIG. 13 illustrates example infrared spectrum 1300 of diffused ambientlight that can be detected by a silicon-based camera according tocertain embodiments. As illustrated, according to the SMARTS model, atnoon in Phoenix, Ariz. during summer time, the IR diffused lightreceived by a SWP filter perpendicular to the horizontal plane is shownby the example infrared spectrum 1300. The total irradiance of theambient light within a wavelength range 750 nm to 1000 nm is about 50.23Watt/m², and thus the power of IR light within the wavelength range andreaching each window (with a diameter of 200 μm) is about 158 nWatt.According to the configuration of SWP filter 1110 shown in FIG. 11A, thetotal power of the ambient IR light illuminating the 15 mm×15 mm eyebox(e.g., square area 1140) from the 8 windows is more than about 600nWatt. To further increase the total power of the IR light illuminatingthe eyebox, SWP filters including a large number of windows arranged inmore complicated array structures may be used.

FIG. 14 illustrates example infrared spectrum 1400 of diffused ambientlight that can be detected by an InGaAs-based camera according to someembodiments. InGaAs-based cameras may have a high responsivity to IRlight within a wavelength range between about 900 nm and about 2500 nm,which includes four IR irradiance peaks of the outdoor ambient light asshown in FIG. 14. The total irradiance of ambient light from 900 nm to2500 nm is about 54.66 Watt/m², which is comparable to the totalirradiance between 750 nm and 1000 nm. In some embodiments, the IRcamera may use Ge, InAsSb, or some nanomaterials based photodetectorsfor IR detection.

FIG. 15 illustrates an example of an eye illumination system 1500 for aneye-tracking system according to certain embodiments. Eye illuminationsystem 1500 may be used to increase the total power of the IR lightilluminating the eyebox (or the user's eye). As described above, thetotal power of the IR light illuminating the 15 mm×15 mm eyebox (e.g.,square area 1140) from the 8 windows of SWP filter 1110 may be more thanabout 600 nWatt, which may or may not be sufficient to achieve a goodsignal to noise ratio in the captured images of the eye. Varioustechniques may be used to increase the total power of the ambient IRlight illuminating the eyebox (or the user's eye). For example, in theexample shown in FIG. 15, eye illumination system 1500 may include anambient light illuminator 1510 that may include a substrate 1520, afirst shortwave-pass (SWP) filter 1530 on one surface of substrate 1520,and a second SWP filter 1540 on an opposite surface of substrate 1520.Substrate 1520 may include a transparent material as described above andmay have any suitable thickness. First SWP filter 1530 and second SWPfilter 1540 may include a thin layer of reflective coating that mayreflect light with wavelengths greater than a threshold value, such asIR light with wavelengths greater than 750 nm, while allowing light withwavelengths shorter than the threshold value to pass through with littleor no loss.

First SWP filter 1530 may include a plurality of windows 1532 (orapertures or holes) through which IR light may pass through and entersubstrate 1520. Second SWP filter 1540 may also include a plurality ofwindows 1542 (or apertures or holes) through which IR light may passthrough and reach a user's eye 1590. The plurality of windows 1532 mayhave a total area larger than the total area of the plurality of windows1542. When ambient light illuminator 1510 is illuminated by ambientlight 1560, some ambient IR light may pass through windows 1532 andenter substrate 1520. A portion of the ambient IR light enteringsubstrate 1520 (as indicated by light ray 1562) may pass through windows1542 and reach user's eye 1590 (as indicated by IR light rays 1570). Aportion of the ambient IR light entering substrate 1520 (as indicated bylight ray 1564) may be reflected by second SWP filter 1540 and first SWPfilter 1530, and may then pass through windows 1542 and reach user's eye1590. In this way, the total power of the ambient IR light passingthrough windows 1542 may be larger than the total power of ambient IRlight passing through windows 850 or 940 shown in FIG. 8 or 9.

Even though not shown in FIG. 15, an antireflective coating may beformed on first SWP filter 1530, and another antireflective coating maybe formed on second SWP filter 1540. The antireflective coatings mayfill the apertures or holes on the SWP filters to form transparentwindows for IR light and visible light. The antireflective coatings mayalso reduce reflection at the interfaces between ambient lightilluminator 1510 and adjacent media, such as air.

In some embodiments, the eye illumination system for eye-tracking in anear-eye display system may include active light source-based (e.g.,using LEDs) eye illumination system in addition to the ambient lightilluminator described above. When the ambient light is strong enough tosufficiently illuminate the user's eye and provide a good image qualityfor the images of the user's eye captured by an IR camera, the activelight source-based eye illumination system may be turned off by acontrol circuit to reduce the power consumption of the eye illuminationsystem. When the ambient light is not sufficiently strong or when thequality of the images of the user's eye captured by the IR camera islow, the active light source-based eye illumination system may be turnedon by the control circuit to illuminate the user's eye using the activelight sources. In some embodiments, the control circuit may include anIR photodetector that can measure the intensity of IR light in ambientlight, and a switch to turn the active light sources on or off based onthe measured intensity of the IR light in the ambient light. In someembodiments, the active light sources may be turned on or off based onthe quality of the images of the user's eye or the results of the eyetracking. In some embodiments, the active light source may be turned onor off manually by the user.

FIG. 16 is a simplified flow chart 1600 illustrating an example of amethod of manufacturing an ambient light eye illuminator for eyetracking according to certain embodiments. The operations described inflow chart 1600 are for illustration purposes only and are not intendedto be limiting. In various implementations, modifications may be made toflow chart 1600 to add additional operations, omit some operations,combine some operations, split some operations, or reorder someoperations.

At block 1610, a shortwave-pass filter may be formed on a first surfaceof a transparent substrate. As described above, the substrate may betransparent to visible light (e.g., light with wavelengths less thanabout 700 nm) and IR light (e.g., light with wavelengths between 750 nmand 2500 nm). The substrate may be flat or may have a curved surface. Insome embodiments, the substrate may be a lens or a waveguide. Theshortwave-pass filter may allow visible light to pass through withlittle or no loss, and may reflect, absorb, diffract, or otherwise blockIR light. For example, the shortwave-pass filter may include a hotmirror. In some embodiments, the hot mirror may include multiple thindielectric layers (i.e., thin films) of different dielectric materialsand/or thicknesses. In some embodiments, the hot mirror may include adiffractive optical element that is transparent to visible light andreflects IR light. For example, the hot mirror may include one or moreFresnel lenses or a meta-grating. In some embodiments, the hot mirrormay include a photonic crystal structure that is transparent to visiblelight and reflects IR light. In some embodiments, the hot mirror may becoated with a layer of material that is transparent to visible light andopaque (e.g., absorptive) to IR light.

Optionally, at block 1620, an antireflective coating and/or a secondshortwave-pass filter may be formed on a second surface of thesubstrate. In some embodiments, the antireflective coating may reducethe reflection of visible light and/or IR light at the second surface ofthe substrate. In some embodiments, a second shortwave-pass filter maybe formed on the second surface of the substrate, where the secondshortwave-pass filter may be similar to the first shortwave-pass filter.In some embodiments, the second shortwave-pass filter may be formed onthe second surface of the substrate and an antireflective coating may beformed on the second shortwave-pass filter. In some embodiments, anantireflective coating may also be formed on the shortwave-pass filteron the first surface of the substrate.

At block 1630, one or more openings (e.g., holes) may be formed (e.g.,cut, etched, drilled, etc.) in the shortwave-pass filter on the firstsurface of the substrate based on a pre-determined pattern. In someembodiments, openings (e.g., holes) may also be formed in one or more ofthe substrate, the antireflective coating, and the second shortwave-passfilter on the second surface of the substrate. In some embodiments, thetotal area of the openings in the shortwave-pass filter on the firstsurface of the substrate may be greater than the total area of theopenings in the second shortwave-pass filter on the second surface ofthe substrate. As described above, the one or more openings may bearranged based on a two-dimensional pattern. For example, the openingsmay be arranged on circumferences of two or more areas (e.g., circular,rectangular, over, or other regular or irregular-shaped areas) that maybe nested or may at least partially overlap. In some embodiments, eachopening may have a diameter equal to or less than 200 μm.

Optionally, at block 1640, the one or more openings (e.g., holes) formedat block 630 may be filled with a transparent material. For example, insome embodiments, an antireflective coating may be formed on the SWPfilter on the first surface of the substrate. In some embodiments,another antireflective coating may be formed on the second SWP filter onthe second surface of the substrate. The antireflective coatings mayfill the apertures or holes on the SWP filters to form transparentwindows for IR light and visible light. The antireflective coatings mayalso reduce reflection at the interfaces between the ambient light eyeilluminator and other media, such as air.

Embodiments of the invention may be used to fabricate components of anartificial reality system or may be implemented in conjunction with anartificial reality system. Artificial reality is a form of reality thathas been adjusted in some manner before presentation to a user, whichmay include, for example, a virtual reality (VR), an augmented reality(AR), a mixed reality (MR), a hybrid reality, or some combination and/orderivatives thereof. Artificial reality content may include completelygenerated content or generated content combined with captured (e.g.,real-world) content. The artificial reality content may include video,audio, haptic feedback, or some combination thereof, and any of whichmay be presented in a single channel or in multiple channels (such asstereo video that produces a three-dimensional effect to the viewer).Additionally, in some embodiments, artificial reality may also beassociated with applications, products, accessories, services, or somecombination thereof, that are used to, for example, create content in anartificial reality and/or are otherwise used in (e.g., performactivities in) an artificial reality. The artificial reality system thatprovides the artificial reality content may be implemented on variousplatforms, including a head-mounted display (HMD) connected to a hostcomputer system, a standalone HMD, a mobile device or computing system,or any other hardware platform capable of providing artificial realitycontent to one or more viewers.

FIG. 17 is a simplified block diagram of an example of an electronicsystem 1700 of a near-eye display system (e.g., HMD device) forimplementing some of the examples disclosed herein. Electronic system1700 may be used as the electronic system of an HMD device or othernear-eye displays described above. In this example, electronic system1700 may include one or more processor(s) 1710 and a memory 1720.Processor(s) 1710 may be configured to execute instructions forperforming operations at a number of components, and can be, forexample, a general-purpose processor or microprocessor suitable forimplementation within a portable electronic device. Processor(s) 1710may be communicatively coupled with a plurality of components withinelectronic system 1700. To realize this communicative coupling,processor(s) 1710 may communicate with the other illustrated componentsacross a bus 1740. Bus 1740 may be any subsystem adapted to transferdata within electronic system 1700. Bus 1740 may include a plurality ofcomputer buses and additional circuitry to transfer data.

Memory 1720 may be coupled to processor(s) 1710. In some embodiments,memory 1720 may offer both short-term and long-term storage and may bedivided into several units. Memory 1720 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 1720 may include removable storagedevices, such as secure digital (SD) cards. Memory 1720 may providestorage of computer-readable instructions, data structures, programmodules, and other data for electronic system 1700. In some embodiments,memory 1720 may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 1720. Theinstructions might take the form of executable code that may beexecutable by electronic system 1700, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on electronic system 1700 (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, memory 1720 may store a plurality of applicationmodules 1722 through 1724, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 1722-1724 may includeparticular instructions to be executed by processor(s) 1710. In someembodiments, certain applications or parts of application modules1722-1724 may be executable by other hardware modules 1780. In certainembodiments, memory 1720 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 1720 may include an operating system 1725loaded therein. Operating system 1725 may be operable to initiate theexecution of the instructions provided by application modules 1722-1724and/or manage other hardware modules 1780 as well as interfaces with awireless communication subsystem 1730 which may include one or morewireless transceivers. Operating system 1725 may be adapted to performother operations across the components of electronic system 1700including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 1730 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 1700 may include oneor more antennas 1734 for wireless communication as part of wirelesscommunication subsystem 1730 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 1730 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15x, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 1730 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 1730 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 1734 andwireless link(s) 1732. Wireless communication subsystem 1730,processor(s) 1710, and memory 1720 may together comprise at least a partof one or more of a means for performing some functions disclosedherein.

Embodiments of electronic system 1700 may also include one or moresensors 1790. Sensor(s) 1790 may include, for example, an image sensor,an accelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 1790 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or some combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or some combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 1700 may include a display module 1760. Display module1760 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system1700 to a user. Such information may be derived from one or moreapplication modules 1722-1724, virtual reality engine 1726, one or moreother hardware modules 1780, a combination thereof, or any othersuitable means for resolving graphical content for the user (e.g., byoperating system 1725). Display module 1760 may use liquid crystaldisplay (LCD) technology, light-emitting diode (LED) technology(including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.), lightemitting polymer display (LPD) technology, or some other displaytechnology.

Electronic system 1700 may include a user input/output module 1770. Userinput/output module 1770 may allow a user to send action requests toelectronic system 1700. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 1770 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 1700. In some embodiments, user input/output module 1770 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 1700. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 1700 may include a camera 1750 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. Camera 1750 may also be used to take photos or videos ofthe environment, for example, for VR, AR, or MR applications. Camera1750 may include, for example, a complementary metal-oxide-semiconductor(CMOS) image sensor with a few millions or tens of millions of pixels.In some implementations, camera 1750 may include two or more camerasthat may be used to capture 3-D images.

In some embodiments, electronic system 1700 may include a plurality ofother hardware modules 1780. Each of other hardware modules 1780 may bea physical module within electronic system 1700. While each of otherhardware modules 1780 may be permanently configured as a structure, someof other hardware modules 1780 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 1780 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 1780 may be implemented insoftware.

In some embodiments, memory 1720 of electronic system 1700 may alsostore a virtual reality engine 1726. Virtual reality engine 1726 mayexecute applications within electronic system 1700 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or some combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 1726 may be used for producing a signal (e.g.,display instructions) to display module 1760. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 1726 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 1726 may perform an action within an applicationin response to an action request received from user input/output module1770 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 1710 may include one or more GPUs that may execute virtualreality engine 1726.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 1726, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 1700. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 1700 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

What is claimed is:
 1. An eye illumination system for eye tracking in anear-eye display system, the eye illumination system comprising: asubstrate transparent to both visible light and infrared light andconfigured to be placed in front of an eye of a user of the near-eyedisplay system; and a shortwave-pass filter coupled to a first surfaceof the substrate, the shortwave-pass filter comprising: regionsconfigured to transmit a first portion of visible light and reflect afirst portion of infrared light found in ambient light entering the eyeillumination system; and a plurality of windows configured to transmitboth a second portion of visible light and a second portion of infraredlight, found in the ambient light entering the eye illumination system,to the eye of the user.
 2. The eye illumination system of claim 1,wherein the shortwave-pass filter comprises a plurality of dielectriclayers, a diffractive optical element, or a reflective material layer.3. The eye illumination system of claim 1, wherein the shortwave-passfilter is configured to reflect ambient light within a wavelength rangebetween 750 nm and 2500 nm.
 4. The eye illumination system of claim 1,wherein the plurality of windows is arranged according to atwo-dimensional pattern.
 5. The eye illumination system of claim 1,wherein the plurality of windows is arranged on circumferences of two ormore areas of the shortwave-pass filter.
 6. The eye illumination systemof claim 5, wherein the two or more areas include an overlapped region.7. The eye illumination system of claim 1, wherein each window of theplurality of windows is characterized by a diameter equal to or lessthan 200 μm.
 8. The eye illumination system of claim 1, furthercomprising an antireflective layer on a second surface of the substrateopposite to the first surface or on the shortwave-pass filter.
 9. Theeye illumination system of claim 1, further comprising a secondshortwave-pass filter on a second surface of the substrate opposite tothe first surface, wherein: the second shortwave-pass filter includesregions configured to transmit visible light and reflect infrared light;and the second shortwave-pass filter includes a set of windowsconfigured to transmit both visible light and infrared light.
 10. Theeye illumination system of claim 9, wherein the plurality of windows ofthe shortwave-pass filter on the first surface of the substrate isaligned with the set of windows of the second shortwave-pass filter onthe second surface of the substrate.
 11. The eye illumination system ofclaim 9, wherein a total area of the plurality of windows of theshortwave-pass filter on the first surface of the substrate is greaterthan a total area of the set of windows of the second shortwave-passfilter on the second surface of the substrate.
 12. The eye illuminationsystem of claim 1, wherein the substrate includes a curved or a flatsurface.
 13. The eye illumination system of claim 1, wherein thesubstrate comprises at least one of a glass, quartz, plastic, polymer,ceramic, or crystal.
 14. The eye illumination system of claim 1, furthercomprising: a light source configured to illuminate the eye of the user;and a control circuit configured to turn off the light source upondetermining that a light intensity of the ambient light is greater thana threshold value.
 15. An eye-tracking system in a display device, theeye-tracking system comprising: an infrared camera; a substratetransparent to both visible light and infrared light and configured tobe placed in front of an eye of a user of the display device; and ashortwave-pass filter coupled to a first surface of the substrate, theshortwave-pass filter comprising: regions configured to transmit a firstportion of visible light and reflect a first portion of infrared lightfound in ambient light entering the eye tracking system; and a pluralityof windows configured to transmit both a second portion of visible lightand a second portion of infrared light, found in the ambient lightentering the eye tracking system, to the eye of the user, wherein theinfrared camera is configured to capture infrared light reflected by theeye of the user.
 16. The eye-tracking system of claim 15, wherein theshortwave-pass filter comprises a plurality of dielectric layers, adiffractive optical element, or a reflective material layer.
 17. Theeye-tracking system of claim 15, wherein each window of the plurality ofwindows is characterized by a diameter equal to or less than 200 μm. 18.The eye-tracking system of claim 15, further comprising a secondshortwave-pass filter on a second surface of the substrate opposite tothe first surface, wherein: the second shortwave-pass filter on thesecond surface of the substrate includes regions configured to transmitvisible light and reflect infrared light; the second shortwave-passfilter includes a set of windows configured to transmit both visiblelight and infrared light; and a total area of the plurality of windowsof the shortwave-pass filter on the first surface of the substrate isgreater than a total area of the set of windows of the secondshortwave-pass filter on the second surface of the substrate.
 19. Theeye-tracking system of claim 15, further comprising an antireflectivelayer on a second surface of the substrate opposite to the first surfaceor on the shortwave-pass filter.
 20. The eye-tracking system of claim15, further comprising: a light source configured to illuminate the eyeof the user; and a control circuit configured to turn off the lightsource upon determining that a light intensity of the ambient light isgreater than a threshold value.